The teenager was on her way back from Taverham High School when she and a friend were confronted by a man before he got into a white van.

The girl’s mother, who wants to remain anonymous, said her daughter had been left traumatised and scared to go out on her own after the incident, which happened on Monday.

She said her daughter was walking home across a field where she and her friend saw a man who exposed himself to them as they walked past.

The mother said: “They saw him go back into his van. It was a white van and they just ran until they got to some people.

“I know she wasn’t physically hurt or anything like that, but it’s just thinking of someone doing something like that – you just don’t expect it round here.”

Teachers at the school are believed to have sent letters home to parents giving advice to pupils about how to stay safe on their way to and from school following the incident.

A spokesman for Norfolk police confirmed they were investigating after receiving a report of indecent exposure alleged to have taken place some time between 3.30pm and 4pm on Monday, May 19.

The spokesman said a man in his 40s was alleged to have exposed himself before making off in a white coloured transit-style van and urged anyone with information to call them.

The girl’s mother said: “I want to make sure people are aware of it. I would hate for people not to know and for anything to happen – I would hate to have that on my conscience.”

Headteacher Peter Whear said: “We had received reports of an incident that occurred outside school earlier this week. The matter was brought to our attention by some of our students and we immediately reported the matter to the police.

“We have worked closely with them to support this investigation.

“We are confident that the matter is in hand and therefore chose to adopt a low-key approach that ensured our students were informed without causing unnecessary alarm.

“Our students learn to make sensible choices and we reminded them at the end of the day on Thursday to stay safe on their journey to and from school by walking or cycling home with friends.”